This invention relates to a novel zoom lens and image pickup apparatus, and more particularly to a zoom lens and an image pickup apparatus which have a hand shake correction function and suppress deterioration of a performance which occurs upon image shifting while the variation power is high.
Conventionally, as a recording method of a camera, a method is known wherein a subject image formed on a surface of an image pickup device formed using a photoelectric conversion element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) element is recorded by converting light amounts of the subject image into electric outputs by means of the photoelectric conversion elements.
Together with the technical progress of the fine working techniques in recent years, higher speed operation of a central processing unit (CPU) and higher integration of storage media are achieved, and such a large amount of image data as have not been able to be handled can now be processed at a high speed. Also for light receiving elements, higher integration and miniaturization is achieved, and the high integration makes it possible to achieve recording of higher spatial frequencies and the miniaturization makes it possible to achieve miniaturization of the entire camera.
However, such high integration and miniaturization as described above reduces the light receiving area of each photoelectric conversion element and hence decreases the electric output of the same, which gives rise to a problem of increase of the influence of noise. In order to prevent this, such a countermeasure has been taken as to increase the amount of light which arrives at the light receiving elements by increasing the aperture ratio of the optical system or disposing very small lens elements (that is, a microlens array) immediately in front of the light receiving elements. The microlens array introduces a flux of light, which is to come to a boundary between each adjacent elements, to the elements. Instead, the microlens array provides a restriction to the position of the exit pupil of the lens system. In particular, if the position of the exit pupil of the lens system moves toward a light receiving element, then the angle defined by a main light ray, which comes to the light receiving element, and the optical axis becomes great and an off-axis light flux directed toward peripheral portions of the light receiving element is provided with a great angle with respect to the optical axis. As a result, the off-axis light flux does not come to the light receiving element, resulting in shortage of the light amount.
A known zoom lenses suitable for a video camera or a digital still camera for recording a subject image is a zoom lens of a four-group configuration having positive, negative, positive and positive groups.
The zoom lens of a four-group configuration having positive, negative, positive and positive groups includes a first lens group having a positive refracting power, a second lens set having a negative refracting power, a third lens group having a positive refracting power and a fourth lens group having a positive refracting power, disposed in order from the object side. When the lens position state changes from the wide angle end state to the telephoto end state, the first and third lens groups are fixed in the direction of the optical axis while the second lens group moves toward the image side to perform a power variation operation and the fourth lens group acts to compensate for the variation of the image plane position which is caused by the movement of the second lens group.
An exemplary one of such four-group zoom lenses including four groups having positive, negative, positive and positive refracting powers is disclosed in Japanese Patent Laid-open No. Hei 6-337353 (hereinafter referred to as Patent Document 1).
Incidentally, an optical system having a high zoom ratio exhibits a reduced angle of view in a telephoto end state thereof, and therefore has a problem that a large blur occurs with an image even by a small hand shake.
An optical hand shake correction system is known as one of hand shake correction systems for correcting a blur of an image by a hand shake or the like.
The optical hand shake correction system uses a lens shift method wherein part of the lens system is shifted in a direction perpendicular to the optical axis, a variable apical angle prism method wherein the apical angle of a prism disposed immediately before the lens system is varied, or some other method. However, since the variable apical angle prism is disposed on the object side with respect to the first lens group which is largest in the lens system, the variable apical angle prism method has a subject to be solved where it is tried to achieve miniaturization including also a driving system.
The optical system of the lens shift type can function as an optical hand shake correction system which includes a combination of a detection system for detecting a shake of a camera caused by such a hand shake as may arise from a shutter release, a control system for providing a correction amount to the lens position based on a signal outputted from the detection system and a shift driving system for driving the shift lens based on an output of the control system and wherein a blur of an image caused by a shake of the camera is corrected by shifting of the lens by the driving system.
Such an optical system of the lens shift type as described above is disclosed, for example, in Japanese Patent Laid-open No. 2002-244037 (hereinafter referred to as Patent Document 2), Japanese Patent Laid-open No. 2003-228001 (hereinafter referred to as Patent Document 3), Japanese Patent Laid-open No. 2002-162563 (hereinafter referred to as Patent Document 4) or Japanese Patent Laid-open No. 2003-295057 (hereinafter referred to as Patent Document 5).
In the optical systems of the documents mentioned above, the entire third lens group disposed in the proximity of an aperture stop or some lens of the third lens group can be shifted in a direction substantially perpendicular to the optical axis to shift the image.
Since the third lens group is fixed in the direction of the optical axis, the shift driving system which is greater in a diametrical direction than the lens diameter can be fixed in the direction of the optical axis. Therefore, the optical system of the lens shift type is suitable for miniaturization of the entire system.
In the zoom lens disclosed in Patent Document 5, the entire third lens group is shifted to shift the image.
In the zoom lenses disclosed in Patent Document 3 and Patent Document 4, the third lens group is formed from a positive sub group and a negative sub group, and the positive sub group is shifted to shift the image.
In the zoom lens disclosed in Patent Document 2, the third lens group is formed from a negative sub group and a positive sub group, and the positive sub group is shifted to shift the image.